Conveyance of webs in a continuous manufacturing process utilize splicing apparatus which joins an expiring (conveying) web to the leading edge of a new (entering) web at zero speed. Accumulators, or take-ups, are generally used to allow the manufacturing line to continue at production speed while the splicing process is completed at zero speed. In the manufacture of sensitized film and paper products, a precision uniform splice gap is required to insure trouble-free conveyance and reduce probability of splice related coating disturbances. In many zero speed butt splicing processes, the leading edge of the new web is overlapped with the trailing edge of the expiring web, both webs are clamped and a knife/cutter assembly trims both ends via a cross-cut. Splice tape is applied over the cut with no provision for generating a slight gap between the cut ends of the web.
Automated zero speed butt splicing equipment is used in many converting applications to join together two webs, a new web and progressing (or expiring) web, allowing continuous operation of the manufacturing line. Butt splicing equipment is also commonly used in manufacture of sensitized film and paper products, where splice characteristics can adversely affect the applied emulsion coatings. In most applications, no provision is made to produce a splice with uniform and specific gap dimensions. Lack of this capability on butt splicing equipment used in the manufacture in sensitized film and paper products can produce splices which can cause coating imperfections and conveyance related problems. Splices which are overlapped, for example, will cause coating imperfections due to a disruption in the coating process. Such disruptions are attributed to the increased thickness as the splice conveys through the coating station. A second cause of coating disturbances is due to non-uniform splice gap, which can generate coating imperfections which are generally persistent as the web continues to convey. A splice without a gap of sufficient width will hinge, i.e., buckle at the point of connection, when conveyed over a roller. This hinging of the web progressively weakens the splice tape at the hinge line (web connection line) as the web is conveyed over successive rollers. Of course, the probability of web tearing also increases with hinging. These problems are very costly and can result in significant waste and unscheduled machine down time.
Various attempts have been made in the prior art to minimize the problems described above. For instance, U.S. Pat. No. 4,120,739 discloses splice gap setting capability (refer to column 7, lines 4-21) which consists of a butt control bar which advances until its free edge contacts the web and introduces a slight bow in the web, which is clamped. This system requires the cut-off edge of the web to be pulled through the clamp, which can create significant web tension and induce tearing. Clamping pressure is adjusted to prevent web tearing as the web is pulled through. However, due to non-uniformity in the web, such as planarity and camber, prevention of tearing and the ability to generate uniform splice gap width are questionable using this method described in this invention. Differences in elasticity of webs used with this process may also result in gap width variability. The patent states gap setting capability is between 0.1 and 0.3 mm.
In U.S. Pat. Nos. 5,468,321 and 3,554,842 butt splicing apparatus is disclosed that lacks an active splice gapping capability for solving the aforementioned problems.
In U.S. Pat. No. 4,769,098, a butt splice apparatus has a method for moving the held portion of the new web from a first position to a second position where it is closely adjacent to the stopped portion of the expiring web (refer to column 4, lines 8-19). There is no provision for positioning the webs for a pre-selected gap setting therebetween.
Therefore, there persists a need for an apparatus and method for joining webs that forms a gap of predetermined width between the webs prior to splicing that is easy to use, reliable, and eliminates web defects usually associated with high production speed splicing operations.